JGEEBILS Biology Entrance Questions and Answers

1. Fruitflies have a red eye colour that is determined by the gene RED. Allele R gives a red eye and allele r gives a white eye. R is dominant over r. A single red eye parent and a single white eye parent were mated. Only 50% of the resulting progeny had red eyes. With respect to the RED gene, which of the following best describes the genotype of the red eyed parent?

a. rr

b. Rr

c. RR

d. Any of the above

2. The pI of a protein is 8.3. To carry out ion-exchange chromatography of this protein at pH=7.0, the following should be used to ensure binding and fractionation:

a. Cation exchanger resin

b. Anion exchanger resin

c. Reactive ion exchanger resin

d. Polyanion exchanger resin

3. Genetic sequence data were used to construct the following evolutionary tree relating Mus muculus, Rattus rattus and Homo sapiens. Which of the following is NOT true?

a. Mice are descended from the last common ancestor of humans and rats.

b. Rats are descended from the last common ancestor of humans and mice

c. Humans are descended from the last common ancestor of rats and mice

d. Humans, mice, and rats have a common ancestor

4. A significant proportion of students at TIFR seem to have descended from Chengis Khan. This information was inferred from:

a. Mitochondrial DNA b. Single Nucleotide Polymorphisms

c. Y chromosome analysis

d. Ancient DNA

5. The recognition sequence for the restriction endonuclease AstWI is GRCGYC where R is any Purine and Y is any Pyrimidine base. In a truly random DNA sequence what will be the average distance (measured in base pairs) between successive AstWI cut sites?

a. 1024

b. 512

c. 4096

d. 24

6. Jitesh carried out a steady-state kinetics experiment for an enzyme degradase with and without molecule X as part of the reaction mixture. The reactions were carried out for 5 minutes and he got the following results:

These results suggest that:

a. Molecule X is a competitive inhibitor

b. Molecule X is an allosteric inhibitor

c. Molecule X is a cofactor

d. Molecule X has no effect on catalysis

7. Irshath is recording the electrical activity of neurons in a cat when the cat is shown light bars at various angles. Two neurons respond to these light bars in the following manner: What can you infer from the above data?

a. Bar angle does not affect neural response in Neuron1 or 2

b. A bar at 50 degrees elicits no response in either of the two neurons

c. A bar at 20 degrees elicits 50% of the maximal response in Neuron 2

d. For any given angle the difference in response levels of Neuron1 and 2 is a constant.

8. In the northeastern states of India, Yaks are a common species. Additionally, cows are also present as well as hybrids between Yaks and cows. The following figure represents genetic variation at ‘cow’ specific and ‘Yak’ specific genetic loci.Which one of the following statements is true?

a. Most animals are hybrids

b. Most animals either Yaks or cows

c. There are more cows than Yaks

d. All hybrids have the same proportion of Yak versus cow genes in their genome

9. A student conducted an experiment where CO2 and N2 were bubbled through water in beakers A and B respectively. He recorded the pH in each of the solutions every 5 min. What is the most valid conclusion the student could draw from these results:

a. The change in pH was too small to be significant b. Bubbling CO2 through water makes it more acidic c. Bubbling N2 through water makes it more acidic d. Both CO2 and N2 make water more acidic.

10. Experiments were carried out on plants living in different environments to measure the size of leaf stomata. Previous investigations have shown that plants transpire more water when the size of stomata is larger. Which of the graphs best represents a plant living in a dry environment?

a. A b. B c. C d. D

11. Champa is trying to characterize a gene s4, which has been previously implicated in early development in mice. Her attempts to characterize the phenotype failed because embryos from crossed homozygous mutant parents did not survive. However, she was able to get some viable homozygous embryos when heterozygous parents were crossed. Which of the following can explain this observation?a. s4 is a critical gene for early development and is maternally required* b. s4 is a critical gene for early development and is an imprinted gene

c. Both a and b

d. None of the above.

12. Alzheimers’ protein-A multimerizes at pH 2 to form aggregates which leads to Alzheimers’ disease. In the brain the pH is always neutral ~7. So what leads to aggregation of A that induces Alzheimers’ in people greater than 60 years of age?

a. Older brains are more acidic.

b. At pH 7, there will be very fast kinetic equilibrium between oligomers and monomers which can change with age to induce aggregation

c. At pH 7, the reaction does proceed to oligomerization but the rate is so low that it takes 60 years to form aggregates

d. Aggregates form during intermittent drops in pH throughout your life.

13. Mutations in two genes x and y in a diploid organism when present togather cause lethality. Which of the following may be inferred about the nature of the gene product?

a. The product of the genes function as an oligomer

b. The two genes fall in the same complementation group

c. None of above d. The product is a homo-oligomer

14. A gene is transcribed at the maximum rate of k per second, and codes for a transcription factor (TF). This transcription factor inhibits the transcription of its own gene, and this is the only way this gene and TF are regulated. Which of the following graphs is most likely to describe how the steady-state concentration of the TF depends on the value of k?

a. A and C b. C c. B d. D

15. Genes X, Y and Z are located on one chromosome. Cross-over frequency between three genes is:

Cross over Frequency Gene Pairs

36% X-Z

10% Y-Z

26% X-Y

Which one of the following best represents the gene location on the chromosome?

Answers
1. b. Rr
2. a. Cation exchanger resin
3. c. Humans are descended from the last common ancestor of rats and mice
4. a. Mitochondrial DNA
5. a. 1024
6. a. Molecule X is a competitive inhibitor
7. c. A bar at 20 degrees elicits 50% of the maximal response in Neuron 2
8. b. Most animals either Yaks or cows
9. b. Bubbling CO2 through water makes it more acidic
10. D
11. a. s4 is a critical gene for early development and is maternally required*
12. c. At pH 7, the reaction does proceed to oligomerization but the rate is so low that it takes 60 years to form aggregates
13. a. The product of the genes function as an oligomer
14. b. C
15.b. Z-Y-X